SILICATES FOR GROUND CONSOLIDATION Silicate based grouts usually contain three main components: Sodium silicate Hardener or reagent Water.

SILICATES FOR GROUND CONSOLIDATION

Silicate based grouts usually contain three

main components:

• Sodium silicate

• Hardener or reagent

• Water

CHEMICAL REACTION BETWEEN SILICATE AND HARDENER

(CH2)m(COOCH3)2 + H2O (CH2)m(COOH)2 + 2 CH3OH

(CH2)m(COOH)2 + SiO2, Na2O n SiO2 + x H2O +

(CH2)m(COONa)2

hydrolysis

gel formation

FACTORS TO BE CONSIDEREDFACTORS TO BE CONSIDERED

• Initial grout viscosity and the viscosity profile during gelation

• Setting time of the grout

• Effect of temperature

• Degree of neutralization of the gel

• Nature of treatment required e.g. water proofing, short or long term consolidation

• Nature of the grout to be treated

GROUT VISCOSITYGROUT VISCOSITY

For a given temperature, the initial viscosity of a silicate grout depends on:

• Type of silicate used (ratio, % solids)

• Ratio silicate/water

• Amount of hardener

INITIAL VISCOSITYINITIAL VISCOSITY

Initial ViscosityStandard sodium Silicate with R100

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

0 2 4 6 8 10 12 14 16 18

Hardener R100 [vol%]

Init

ial V

isc

os

ity

[m

.Pa

.s]

30 vol% Sodium Silicate 40 vol% Sodium Silicate 50 vol% Sodium Silicate 60 vol% Sodium Silicate

INITIAL VISCOSITYINITIAL VISCOSITY

Initial Viscosity

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

18,0

20 30 40 50 60 70 80

Sodium Silicate [vol%]

Init

ial V

isc

os

ity

[m

.Pa

.s]

10 vol% R100 5 vol% R100

SETTING TIMESETTING TIME

The grout setting time depends on:

• Nature of silicate; the higher the ratio the longer the setting time. The higher the solid content of the silicate the shorter the setting time, assuming a constant degree of neutralization

• Concentration of the silicate; at constant volumetric dosages of hardener, the setting time increases with increasing silicate levels.

• Type of hardener and concentration of hardener

• Grout and soil temperature; the higher the temperature the shorter the setting time

• Nature of the soil; acidity of the soil, calcium/magnesium content in the soil could influence the setting time

SETTING TIMESETTING TIME

Sodium Silicate Ratio 3.3Setting times at 20 C

30,0

35,0

40,0

45,0

50,0

55,0

60,0

65,0

4 5 6 7 8 9 10

R100 [%vol]

Se

ttin

g t

ime

[m

in]

30 %vol Sil 35 %vol Sil 40 %vol Sil 50 %vol Sil 60 %vol Sil

TEMPERATURE VS. SETTING TIMETEMPERATURE VS. SETTING TIME

R100/Silicate Temperature versus Setting time

15

20

25

30

35

40

45

50

55

60

10 15 20 25 30 35

Temperature [C]

Se

ttin

g t

ime

[m

in.]

DEGREE OF NEUTRALIZATIONDEGREE OF NEUTRALIZATION

In general the higher the degree of neutralization the higher the mechanical

strength (compressive strength) the higher the durability.

Degree of Neutralization = (VH * dH * 6200)/(VS * dS * NA) * MH

VS = silicate volume (l)

dS = density of silicate (S.G)

NA = weight % alkali (Na2O) in silicate

MH = molecular weight of hardener

VH = volume of hardener (l)

dH = density of hardener (S.G.)

DEGREE OF NEUTRALIZATIONDEGREE OF NEUTRALIZATION

% Alkali NeutralizedStandard sodium Silicate with R100

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16 18

Hardener R100 [vol%]

Alk

ali

Ne

utr

aliz

ed

[%

]

30 vol% Sodium Silicate 40 vol% Sodium Silicate 50 vol% Sodium Silicate 60 vol% Sodium Silicate

COMPRESSIVE STRENGTHCOMPRESSIVE STRENGTH

Compressive Strength at 7 daysSilicate Grouted Leighton Buzzard Sand (grade 14/25)

0

500

1000

1500

2000

2500

3000

3500

4000

4 5 6 7 8 9 10 11

Hardener R100 [vol%]

Co

mp

res

siv

e S

tre

ng

th [

kN

/m2

]

30 vol% Sodium Silicate 35 vol% Sodium Silicate 40 vol% Sodium Silicate

50 vol% Sodium Silicate 60 vol% Sodium Silicate 70 vol% Sodium Silicate

COMPRESSIVE STRENGTHCOMPRESSIVE STRENGTH

Compressive Strength Development at 7 daysSilicate Grouted Leighton Buzzard Sand (grade 14/25)

0

500

1000

1500

2000

2500

3000

3500

4000

20 30 40 50 60 70 80

Sodium Silicate [vol%]

Co

mp

res

siv

e S

tre

ng

th [

kN

/m2

]

10 vol% R100 5 vol% R100

INITIAL VISCOSITY VS. COMPRESSIVE STRENGTHINITIAL VISCOSITY VS. COMPRESSIVE STRENGTH

Initial Viscosity versus Compressive Strentgth

y = 92,08e0,2041x

R2 = 0,9115

0

500

1000

1500

2000

2500

3000

3500

4000

0,0 2,0 4,0 6,0 8,0 10,0 12,0 14,0 16,0 18,0

Initial Viscosity [m.Pa.s]

Co

mp

res

siv

e S

tre

ng

th [

kN

/m2

]

SYNERESISSYNERESIS

Syneresis is the phenomenon of the reaction of

silanol groups whereby a siloxane bond will be

formed and water will be released. This loss of water

leads to shinkage and/or distortion of the silica gel

structure.

Si

O - H

Si

HO

Si Si

O

H2O

DEGREE OF SYNERESISDEGREE OF SYNERESIS

Main factors influencing degree of syneresis:

• Silicate ratio (ratio > = Syn <)

• Degree of neutralisation (neutralization > = Syn <)

• SiO2 content of the grout formulation

(SiO2 content > = Syn >)

DEGREE OF SYNERESISDEGREE OF SYNERESIS

Degree of Syneresis vs. %vol Silicate Ratio 3.3 at 70% Neutralization

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80

Silicate [% vol]

De

gre

e o

f S

yn

ers

es

is [

%]